Process for the beneficiation of phosphate rock



uly 1967 I J. D. CLARY ETAL 3,

PROCESS FOR BENEFICIATION OF PHOSPHATE ROCK Filed 001',- 10. 1963 INVENTORS J. D. CLARY E.J.' O'BRIEN J A. NOTARY BY Mm 27 M ATTORNE United States Patent Connecticut Filed Oct. 10, 1963, Ser. No. 315,164 7 Claims. (Cl. 241-) This application is directed to the beneficiation of phosphate ores. In particular, this invention is directed to a novel process for separating the valuable phosphate rock from the clay and sand contained in naturally occurring phosphate ores, wherein the phosphate ore is disintegrated while in a substantially dry condition.

When phosphate ore is mined from the earth, it is referred to as a matrix. This matrix is comprised of pieces of phosphate rock and silica which are admixed in a claylike material which is denoted as slimes. In order toobtain a phosphate rock which is usable in the production of fertilizer products, such as superphosphate, triple superphosphate, etc., or other products such as phosphorous or phosphoric acid, it is necessary to remove substantially all of the siliceous and clay-like material from the matrix.

The prior art has disclosed numerous processes and means which are employed to obtain a phosphate rock which is free of slimes and silica. In general, most all of these processes utilize a complex system of screening and surface washing in conjunction with table and froth flotation steps which further increase the efliciency of the re covery process.

In order to operate an eflicient beneficiation process,

the matrix material must be distintegrated as much as possible prior to attempting to recover the phosphate rock from the silica and clay. In order to distintegrate the matrix, the present practice is to slurry the matrix with water and then to subject it to a series of screening, abrasion, and washing steps. The matrix Will then be disintegrated sufliciently to permit the subsequent removal of the sand and slimes through the use of conventional phosphate recovery processes and apparatus. Such processes usually involve first screening the distintegrated matrix to recover the large phosphate rock particles and to separate the extremely fine 150 mesh) particles and slimes from the matrix. The slimes and fine particles are disposable materials. The fine material (14 mesh to +150 mesh) which passes through the initial screening step is then subjected to table and cell flotation processes to recover small and intermediate sized phosphate particles.

One of the major problems which is encountered in using the above described process is that of the disposable clay slimes and fine siliceous particles which are separated from the phosphate matrix. These slimes must be separated from the matrix prior to subjecting the matrix to the table and flotation treatment, for the slimes have extremely large surface areas and tend to absorb chemical reagents, thereby making the flotation cost prohibitive. The slimes also contain considerable amounts of phosphate, generally analyzing in the range of from 20 to 25% BPL. It is therefore highly desirable to provide a process for the beneficiation of phosphate ores in which this objectional disposal product could be eliminated.

Another acute problem which is encountered in using the process mentioned above is that of the siliceous and clay-like materials adhering to the surface of the phosphate rock. The operating efficiency of this process is dependent upon the removal of substantially all of the materials from the phosphate rock. The siliceous and claylike material which is present in the original phosphate matrix may take the form of mud balls when slurried with water and pumped from the mine site to the washing plant and carry through to the subsequent processing steps with the pieces of phosphate rock of substantially the same size. The mud balls are of two types; a mixture of clay and silica or a mixture of clay, silica, and phosphate rock particles, The mud balls will produce excessive clogging during screening and will cause the loss of a considerable amount of valuable phosphate material. To eliminate the problem of mud balls and surface adhesion, extended and expensive surface washings and expensive disintegration and separation apparatus must be employed.

It is an object of this invention therefore to provide a novel process for beneficiating phosphate ores whereby the above-mentioned problems of the prior art are avoided. Specifically, it is an object of this invention to provide a substantially dry process for efliciently and thoroughly distintegrating a phosphate matrix into its major component parts, thereby eflectively preparing the matrix for use in a subsequent phosphate recovery process. Other objects, advantages, and features of this invention will be apparent to those skilled in the art in view of the following more detailed description of the invention.

These and other objects are achieved by means of this invention in whichis provided a substantially dry process for the disintegration of phosphate rock prior to the re-- covery of such. In particular, this process comprises thermally drying a phosphate matrix while simultaneously subjecting the matrix to an attrition effect, air-classifying the dried matrix to produce pebble phosphate and fine particles of phosphate rock, silica, and a small amount of agglomerated clay, and separating the pebble phosphate from the fine particles and recovering same as a final product. The fine particles of phosphate rock are then separated from the fine particles of silica and agglomerated clay by the flotation treatment of the prior art and are subsequently recovered as a phosphate concentrate product. By proceeding in the above manner, the problems of the disposable slimes and the mud balls are eliminated completely.

The invention will be further understood by referring to the accompanying drawing. It should be understood that this drawing is intended to be only a means of illustrating the inventive concept and is not to be considered a limitation of same.

In the drawing, the numeral 1 designates the feed hopper and means to which the phosphate matrix is transported via line 2 from the mine and from which said matrix is conveyed to the attrition column 3. Positioned beneath the columns 3 and in direct communication therewith is a fluidized bed chamber 16. An impingement chamber 4 is positioned above the attrition column and connects said column with a first scrubber collector means 5.

The design of the impingement chamber is important. [he angle between the impinged surface and the direction )f flow of material (gas and solid) impinging on said surface must be sufliciently sharp to produce the required lisintegration of the matrix. In general, said angle may )e within the range of from 60 to 150, with the preferred angle being 90. In lieu of the impingement cham- 361, however, the disintegration chamber may be any au- :ogenous grinding device, such as a Jordan mill or a ball nilling device which is capable of producing the requisite disintegration of the matrix. It is to be understood therefore that any such device is intended to be usable in this invention.

Pneumatic classification occurs within first scrubber col- .ector 5,-Whereby the matrix is separated into a -200 mesh fraction and a +200 mesh fraction. (As used throughout this application, mesh size refers to the U.S. Standard.) The +200 mesh fraction is taken to a dry screen separation means 6 wherein the pebble phosphate material (+14 mesh) is removed through line 7 as a final product. The -14 mesh material, which comprises fine particles of phosphate rock, silica,-and a small amount of agglomerated clay, is removed from the screen separator 6 through line 8 and conveyed to a second screen separation means 9. Within the screen means 9, the matrix is divided into a 14 x +35 mesh fraction which is taken to a table flotation device .10 wherein it is treated in the conventional manner with anionic flotation reagents, which are usually a mixture of fatty acids, kerosene, fuel oil, and caustic soda. From the table flotation device 10, the phosphate concentrate product is removed through line 11 while a disposable product consisting essentially of siliceous material, is removed through line 12 and sent to waste. Within the screen separation means 9, the matrix will also be divided into a 35 x +100 mesh fraction which is taken to the first cell 22 of the double cell flotation process. In cell 22, this fraction of the matrix is treated with a reagent comprising caustic soda, fuel oil, fatty acids, and if desired, a minor amount of kerosene. Asiliceous disposal product will be separated from the phosphate and removed through line 24 and sent to waste. The phosphate concentrate from this flotation step is removed through line 23, cleaned with sulphuric acid to remove oil and traces of fatty acid, washed, and conveyed to flotation cell 25; Inthis flotation step, amines are added as reagents. Within cell 25, the particles are divided into a disposable silica product which is removed through line 27 and sent to waste and into a phosphate concentrate possessing very high bone phosphate of lime (BPL) value which is removed through line 26.

The -200 mesh fraction is removed from first scrubber collector and conveyed through line 20 to a second scrubber collector 13 whereinapproximately 95% of the fine material will be recovered and collected. This material will be subsequentlyremoved through line 15. The gases from this collector will be wet-scrubbed and exhausted to the atmosphere through line 14- Line 17 is connected to the fluidized bed chamber 16 for removing therefrom any phosphate matrix which is not sufficiently disintegrated within theattrition column and fluidized bed chamber. This material will be taken to a dry screen 18. The inch material will be removed from the dry screen through line 21 as a final product. The inch material will be removed from the screen through line 19 and recirculated to the feed means.

The process of this invention operates generally as follows. Phosphate matrix is fed via line 2 to hopper and feed means 1 from which it is fed to the attrition column 3. A hot inert gaseous fluid at a temperature of approximately 350 F. and at a velocity of approximately 7,000 feet per minute flows from the fluidized bed chamber up through the vertical attrition column 3. The velocity of the fluid is adjusted such that the matrix which is inch will be forced up the column and into the impingement chamber 4 whereas the inch matrix will fall down the attrition column and into the fluidized bed chamber 16, thereby effectuating pneumatic classification of said matrix (into 4 inch particles) within said attrition column. (As used in this application the term pneumatic classification means the separation of solid material into cuts, or fractions, of desired particle size, or mesh, via a stream of inert gas or gaseous fluid. Stream flow is used to produce said classification within attrition column 3, and centrifugal flow is used for said purpose within first scrubber collector 5. Said inert gas can be any gas or gaseous mixture that does not react with said matrix. Suitable gases include, but are not limited to, air, nitrogen, helium, argon, and combustion gases comprised of nitrogen, carbon dioxide, and water vapor.) The inch matrix is forced through the impingement chamber and into the scrubber collector 5 wherein it is separated into a 200 mesh fraction and a +200 mesh fraction. The +200 mesh fraction is removed from the scrubber collector 5 to a dry screen 6 which separates the matrix into +14 mesh final product pebble phosphate and 14 x +200 mesh fraction comprising fine particles of phosphate rock, silica, and a small amount of agglomerated clay Which is taken through line 8 to a second screen separation means 9. Within the separation means 9, the phosphate matrix is divided into a 14 x +35 mesh fraction which goes to the table flotation means 10 and into a 35 x +200 mesh fraction which is transported to the double cell flotation operation designated by the numerals 22 and 25. Fine phosphate rock concentrate products are produced by these flotation steps and recovered. The disposal products comprising the silica and agglomerated clay are collected and sent to waste.

It is to be understood that the flotation treatment described above can be a multiple pass operation, i.e., one in which the phosphate concentrate product is recycled and reprocessed in order to increase the BPL content of the final product. Such concept is therefore intended to be within the scope of this invention. Similarly by proper screening and control of particle size, it is possible to eliminate the table flotation operation and to use only the double cell (or froth) flotation operation and still recover a product of sufliciently high BPL content. Therefore, this feature is also within the bounds of this invention.

The 200 mesh fraction which is obtained from the scrubber collector 5 is removed through line 20 and conveyed to a second scrubber collector 13, wherein the fine clay-like material is recovered and collected. This material will subsequently be removed from the collector through line 15. The gases from the collector are wetscrubbed and exhausted to the atmosphere through line 14.

The inch phosphate matrix which falls down the attrition column and into the fluidized bed chamber will be disintegrated during the fall by the action of the high temperature gases flowing upward from the bed chamber and into the attrition column. The material on the bed plate will be fluidized by the gases and dried. The clay material will be degraded by the agitation produced while in the fluidized state and will be lifted upward into a contraction chamber opening into the attrition column. This degraded material travels up the attrition column and is processed with the inch material as described above. The material on the bed plate which is not degraded is discharged from the bed plate through line 17 and passes through dry screen 18 wherein the material is separated into a inch fraction, which is removed through line 21 as a final product, and into a inch fraction which is removed through line 19 and recirculated to the feed means 1.

It is thus seen that by proceeding in the above-described manner, a completely integrated process and combination of apparatus is provided for the disintegration and recovery of phosphate ore. The success of this operation depends to a great extent upon the velocity and temperature of the fluid which passes through the fluidized bed chamber and attrition column. The temperature and velocity of this fluid must be adjusted so as .to convey the inch material through the attrition column, impingement chamber, and scrubber collector, thereby disintegrating the material and preparing it for flotation separation. In general, the velocity of this fluid can be in the range of about from 4,000 feet per minute to about 9,000 feet per minute, with the preferred velocity being approximately 7,000 feet per minute. The temperature of the fluid within the attrition column may range from 250 F. to 400 F., with the preferred temperature being 350 F. To maintain this temperature within the column, a temperature range of 2000 F. to 4000 F. should be maintained below the fluidized bed. The higher temperature is required below the fluidized bed in order to compensate for loss of heat due to the moisture contained in the matrix which falls down the column and into the fluidized bed chamber. Any substantially inert gaseous fluid is suitable for usage in this operation. Illustrative examples of such are air combustion gases (comprising carbon dioxide, water vapor, nitrogen, and oxygen), carbon dioxide, nitrogen, argon, helium, etc.

There are numerous advantages to the process and combination of apparatus disclosed by this invention. Perhaps the greatest advantage to be derived is that of the elimination of the disposable slimes problem. The present commercial practice is to pump the slimes into large ponds covering thousands of acres which have been built especially for their disposal. Since these slimes have a great tendency and capacity to absorb Water (approximitely 70 to 80% of their weight) the land on which these slimes are deposited will become completely useless and worthless. This invention would eliminate this problem entirely, thereby resulting in a saving of considerable expense and of land.

This invention also makes it possible to eliminate the pumping of the matrix from the mine torthe washing plant, which is a distance of from 3 to 5 miles or more. To pump the matrix over this distance and to dispose of the slimes from the washing plant and to recycle the water requires over 30 miles of 16 inch pipe (at a cost of from 8 to 10 dollars per foot), twelve pumping units costing 80,000 dollars each, and one-half million dollars of pumping electricity each year. The process and apparatus disclosed herein makes it unnecessary to utilize this elaborate pumping system. Concomitant with this saving on equipment is a significant saving in manpower, since this pumping system constantly requires inspection to detect and to avoid break-downs, leaks in the pipe, etc.

Since the pumping system from the mine to the processing plant has been eliminated by means of this invention, the problem of mud balls forming in the pipe during such transportation is also eliminated. By means of this invention, the matrix will be transported, either by means of a truck or a belt or roller conveyor system of some type, from the mine site to the processing plant. Since the matrix is never slurried with water, there will be no opportunity for the objectionable mud balls to form.

In addition to the above advantages, this invention will eliminate a substantial portion of the complex system of washing and screening which is presently employed in the commercial processes. This will further reduce the cost of production by a considerable extent.

This invention will be better understood by reference to the following specific but non-limiting examples.

EXAMPLE 1 Proceeding as described, Florida phosphate matrix was fed at a rate of approximately 1000 lbs. per hour into the attrition column. Hot (ca. 3000 F.) combustion gases comprising water vapor, carbon dioxide, nitrogen, and oxygen were introduced into the fluidized bed chamber and circulated at a velocity of approximately 7000 feet per minute through the attrition column, thereby producing an equilibrium temperature of about 350 F. in said column. Said combustion gases dried and conveyed all of the phosphate matrix of inch and smaller upward through the attrition column, into and through the impingement chamber, and to the scrubber collector, wherein the matrix was collected and separated into a 200 mesh fraction and a +200 mesh fraction.

The -200 mesh fraction was removed from the scrubber collector and taken to a second collector. The gases from the collector were wet-scrubbed and exhausted to the atmosphere. Approximately 1168 lbs. of fine material was recovered within the collector over a period of 8 hours.

The +200 mesh fraction from the first collector was taken to a dry screen wherein it was separated into +14 mesh and 14 mesh fractions. Approximately 720 lbs. of the +14 mesh was taken off as a pebble phosphate fiinal product. The 14 x +200 mesh fraction, consisting essentially of fine particles of phosphate rock, silica, and a very small amount of agglomerated clay, was taken from the screen in a substantially dry condition to a second dry screen wherein it was separated into 14 x +35 mesh fraction and the +35 x +200 mesh fraction. These fractions were then taken to the table and cell flotation operations, respectively.

In the table separation operation, the l4 x +35 mesh fraction is passed through a series of agitation vessels in which it is admixed with anionic flotation reagents comprising a mixture of fatty acids, kerosene, fuel oil, caustic soda and water. From the agitation vessels, the admixture of the reagents and phosphatic materials is passed over a series of regular ore dressing tables, which are tables with grooved surfaces, the tables being set at a slight angle and vibrated. The oiled phosphate particles will float over the grooves and off the side of the tables, while the siliceous particles will follow the grooves and discharge otf the end :of the tables. Operating over a period of 8 hours, 704 lbs. of phosphate rock and 512 lbs. of disposal products were produced.

The 35 x +200 mesh fraction was taken to the double cell flotation operation. In the first cell, this fraction was admixed with a mixture'of reagents comprising caustic soda, fuel oil, fatty acids, and water. Approximately 6 lbs. of this reagent mixture was used per ton of feed. The phosphate concentrate product which was produced from the first cell was cleaned with a sulphuric acid solution (ca. 3.25 lbs. per ton of feed) to remove oils and traces of fatty acid. The concentrate was then washed again and conveyed to the next bank of flotation cells, in which amines (approximately 0.2 lb.) per ton of feed were added as reagents. In this second flotation step, the siliceous and clay materials were coated by the amine and attached themselves to the air bubbles, leaving the phosphate rock particles in the under flow of the cell. Approximately 1,816 lbs. of phosphate rock concentrate and 2,920 lbs. :of disposal product were obtained.

During the operation of this example, the inch phosphate matrix descended through the attrition column and into the fluidized bed chamber. A large proportion of material Was disintegrated during the fall by the action of the hot, dry gases. This material was forced up the attrition column and processed and collected as described above. Any material collected on the bed plate of the fluidized bed chamber which was not disintegrated was discharged from the fluidized bed chamber and passed through a dry screen wherein the material was separated into a inch fraction, which was removed as a final product, and into a inch fraction, which was re-' moved from the screen and recirculated and reprocessed. During this period of operation, lbs. of inch product was recovered.

Results of screen and chemical analyses of the feedstock are given in Table 'I, and similar data for the product (concentrate) are presented in Table H.

TABLE I.-FEEDSTOCK Weight Percent Assay Material of Feedstock BPL Dis- Retained in tribution 4 Fraction BPL X Insoluble 2 I and A 3 H4 Inch Fraction i. 2.0 72.1 7. 5 2. 3 3. 5 Inch x +14 Mesh Fraction 9.0 74. 2 6. 4 2.1 16. 2 14 x +35 Mesh Fraction. 15. 2 46.1 41. 6 2. 2 16. 9 35 x +200 Mesh Fraction 59. 2 36. 6 61.0 1. 7 52. 4 200 Mesh Fraction i. 14. 6 31. 2 45. 3 12. 7 11.0 Feedstock, Not Screened 41. 3 49. 8 3. 4 100 1 Weight percent bone phosphatc of lime (BPL).

2 Weight percent insoluble material 3 Weight percent Fe and A1 03. 4 To determine the BPL distributi )f feedstock; (b) Screen a 100 g. samp BPL in each fraction, and (c) Galen late the distribution by the formulas 100 x G, 100 x G, 100 x G", etc.

T T T TABLE II.PRODUCT Weight Percent Assay Weight Percent Material of Total Feed Recovery of Retained in Fraction BPL 1 Insoluble I and A 3 Inch Fraction 2.0 72.1 7. 2. 3 100 Inch x +14 Mesh Fraction. 9.0 74. 2 6. 4 2.1 100 14 Mesh x Mesh Fraction 8. 8 72.8 7. 5 2.1 93. 0 -35 Mesh x +200 Mesh Fraction 22. 7 75. 5 3. 5 2. 1 78.0 Total Product 42. 5 74. 5 6.1 2.1 87. 5

1 Weight percent bone phosphate of lime (BPL).

2 Weight percent insoluble material 3 Weight percent Fe Oa-hdlioa.

An analysis of the results of these runs proves that the process and combination produced a phosphate rock BPL content to be suitable for usage in the production of synthetic phosporous, phosphoric acid, fertilizers, or any of the other commercial phosphate products.

EXAMPLE 2 We claim: 1. A process for the hen which comprises:

(a) thermally dryinga phosphate matrix while simultaneously subjecting said matrix to an attrition effect within a vertical attrition column,

(b) pneumatically classifying the dried matrix to produce pebble phosphate and fine particles of phosphate rock, silica, and a small amount of agglomerated clay,

(c) separating the pebble phosphate from said fine of apparatus of this invention product of sufficiently high 35 eficiation of phosphate rock cell flotation operation.

tion operation.

particles and recovering same as a final product,

((1) separating said fine from said fine particles of silica and agglomerated clay, and

(e) subsequently recovering the fine phosphate rock particles.

said column.

particles of phosphate rock 3. The process of claim 2 in which the pneumatic classification within said vertical column separates said matrix into fractions of inch and inch, the inch fraction passing up the column and the inch fraction falling down said column into a fluidized bed chamber, thereby being in part disintegrated into inch material during said fall, said inch material subsequently being forced up the column and through the beneficiation process of steps (a) through (e) by the gaseous fluid passing therethrough.

4. The process of claim 3 in which the matrix not disintegrated during said fall is removed from said fluidized bed, screened, and recirculated to the attrition column.

5. The process of claim 3 in which pneumatic classification within the first scrubber collector further separates the matrix into a -200 mesh fraction and a +200 mesh fraction prior to separation of the pebble phosphate from said fine particles, and the 200 mesh material is subsequently collected and recovered.

6. The process of claim 1 in which the separation of the fine particles of phosphate rock from the fine particles of silica and agglomerated clay is by means of a table and 7. The process of claim 1 in which the separation of the fine particles of phosphate rock from the fine particles of silica and agglomerated clay is by means of a cell flota- References Cited UNITED STATES PATENTS Stockton 24l18 X Johnson 20912 Houston 20912 Jackering 24l18 X WILLIAM W. DYER, 111., Primary Examiner.

H. F. PEPPER, 111., D. KELLY, Assistant Examiners. 

1. A PROCESS FOR THE BENEFICIATION OF PHOSPHATE ROCK WHICH COMPRISES: (A) THERMALLY DRYING A PHOSPHATE MATRIX WHILE SIMULTANEOUSLY SUBJECTING SAID MATRIX TO AN ATTRITION EFFECT WITHIN A VERTICAL ATTRITION COLUMN, (B) PNEUMATICALLY CLASSIFYING THE DIRED MATRIX TO PRODUCE PEBBLE PHOSPHATE AND FINE PARTICLES OF PHOSPHATE ROCK, SILICA, AND A SMALL AMOUNT OF AGGLOMERATED CLAY, (C) SEPARATING THE PEBBLE PHOSPHATE FROM SAID FINE PARTICLES AND RECOVERING SAME AS A FINAL PRODUCT, (D) SEPARATING SAID FINE PARTICLES OF PHOSPHATE ROCK FROM SAID FINE PARTICLES OF SILICA AND AGGLOMERATED CLAY, AND (E) SUBSEQUENTLY RECOVERING THE FINE PHOSPHATE ROCK PARTICLES. 